Electron tube circuits



u y 9 3 I P. N. MARTIN 2,645,716

ELECTRON TUBE cmcuns Filed Dec. 1, 1951 55 CT 59 0 Pa 15!??? so To A.C. 451

E 57 45 19 .9 11 21 R5 59 i HIS ATTORITY Patented July 14, 1953 ELECTRON TUBE cmourrs "Paul N. Martin, Penn Township, Allegheny County, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Original application August 24, 1948, Serial No.

45,937. Divided and this application December'l, 1951, Serial No. 259,399

1 Claim. (Cl. 2511-27) l My invention relates to electron tube circuit and particularly to electron tube circuits ar' ranged toprovide safe operation of the-circuits and apparatus associated therewith. I

. The present application is 'adivision of my copending application for United States Letters Patent, Serial No. 45,937, filed August 24, 1948, l for Electron Tube Circuits.

- For the purposes of this disclosure, it is to be understood that the term electron tube shall mean an electron discharge device comprising-an enclosure containing therein two' or more electrodes and being either highly evacuated or filled with gas at a low pressure, while the term gas tube shall specifically mean an electron tube filled with gas at a low pressure.

In certain applications of electron tube circuit suchas, for example, relay control circuits for railway signaling systems, it is essential to insure that the relay governed by the electron tube will pick up when and only when acontrol voltage of particular character is supplied to the input circuit of the electron tube which has the'relay winding connected to its anod circuit. A bias voltage is generally provided for preselecting the operating characteristics of the electron tube circuits, and it is necessary to provide means for checking the continuity ofthe elements by which the bias'voltage is supplied to the tube.

Additionally, it has been found that under certain conditions electron tubes of the gas type will continue to conduct, having once been rendered conductive, if the input circuit to the grid and cathode of the tube is interrupted in such manner that the grid is coupled, capacitively or 7 otherwise, to a possible source of stray voltage.

Another possible cause of improper operation of. gas tube circuits is that of false firing or conduction of the tube due to leakage of'current in the tube base or wiring between the anode and control grid when the normal input circuit between the control grid and cathode of the tube is interrupted.

Accordingly, it is an object of my invention to provide novel and improved electron tubecirbecomes disconnected.

. 2 p Another object of my invention is to provide novel and improved electron tube circuits as ranged to prevent the conductionofthe tube by-' stray voltages supplied to the grid of the tube if the grid-cathode circuit is interrupted. j-

Other objects of my invention and features of novelty thereof will be apparent from the following description taken in connection with the accompanying drawings.

In practicing my invention I provide a circuit arrangement which includes one ormore of the control electrode in a, multi-element electron tube and the source of bias voltage in series with the anode circuit of the tube, and also includes the control circuit for the tube in series therewith, so that the several circuits form a series arrangement, whereby an interruption of any part of the complete circuit prevents the flow of current in the anode circuit and thereby prevents the operationof the. relay in the anode circuit of the tube. Additionally, I provide ,a fourterminal condenser connected in shunt across the input circuit in order to shunt stray voltages while the plates of the condenser are connected as series elements in the input portion of the circuit so that an open connection to the con denser results in a safe failure of the apparatus;

I shall describe one form of apparatus embodying my invention and shall then point out the novel features thereof in claim. In the accompanying drawing,- the single figure is a diagrammatic view showing one form of electron tube circuits embodying my invention which employs a four-element electron tube.

, Referring to the drawing, the reference char- ,acter VTI designates a, four-element indirectly heated gas tetrodeof the thyratron type, having an anode 5, a shield grid 1, a control grid 9, a cathode II and a heater l3. The shield grid 1 of tube VTI is provided with two terminals l5 and I1, and the control grid 9 is also provided with two terminals [9 and 2|, and these grids are arranged so that the grid structure forms a series circuit between the terminals associated with each of the grids. Thus a circuit connected tothe terminals of ,thes grid includes the grid structures and grid connections in series so that any break in the gridsortheirconnections Iwithin the tube will interrupt the circuit. The heater [3 of tube VTI is supplied with energy from a suitable source,not shown.

Power is supplied to the'anode 5 of the tube VTI from a suitable source, here shown as a secondary winding SI having terminals 25 and 21 of a transformer PT, which has its primary winding P connected to a suitable source of alternating current, not shown. A second secondary winding 62 provided with terminals 29 and 3!, provides a suitable source of bias voltage for the shield grid l of the tube VTl. The winding of a relay R and a' limiting resistor RP are connected in series between terminal 25 or secondary. winding S! and the anode 5 of the tube VEi,

and terminal Zlof secondary winding S! is con nected to terminal E5 of the shield grid i; Re-

lay R is of the type having contacts which are slow to release, in order that the contacts ofthe lay R and causes the contact 33 of relay'R to be picked up. As previously explained the relay R is slow in releasing, so that during the alternate half cycles in which the tube VT! is nonconductive, the relay R will continue to hold its front contact 33 closed. Q 1

The conducting condition of tube VT! is pre- 7 determined by the proper arrangement and proportioning of the bias voltage supplied to the shield grid! of tubeVT! from the secondary winding S2 of transformer PT. The bias voltrelay will remain pickedup during the alternate half cycles of the alternating current supplied to the anode circuit of the tube for whichthe tube is non-conductive, and the slow-releasing feature is preferably secured by the use of a cop.-. per ferrule or sleeve on the coreof the relay, 1

which acts as a short-circuited single turn winding, this'type of relay structure reducing the value of'induced voltage generated by the self-inductionof thewinding ofv the relay when the current which flows therethrough-is cut oii. 'A contacti33 of relay R governs a control circuit,

not shown.

age supplied to the shield grid l from the transformer PT is supplied thereto by a circuit one side of which may be traced from terminal 3! of secondary winding S2 through the limiting resistor RS to terminal ll of the shield grid 7, and

the other side of which circuit maybe traced from the'termina'l 29 of secondary winding S2 to the cathode of tube VT! through the con trol grid 9, by way of terminals 2! and !9, the

Terminal :7 of shield grid 7 'or the tube VT! is 7 connected to terminal (ii of the secondary Winding S2 through a current limiting resistor RS, and terminal 29 of the secondary winding S2 is connected to terminal, 2! of the control grid 9 of tube VT! l The tube VT! is governed by a source of alternating current control energy, not shown, which energy is at times supplied to the primary winding of a control transformer CT. -The secondary winding tloi control transformer CT 7 is provided with ,terminalsSQ and M, and terminal 39 is connected to terminal i9 ofthe control grid 9 of tube VT! bya circuit which in-v cludes in series ,a grid resistor RGand one 'plate of, afour-terminal condenser C, thisone. plate having terminals t3 and 45. 1 Terminal 4! of the secondary winding, oftransformer CT is conto the cathode ii, through oneplate of condenser C by way .of terminals 49 and 4'! to the terminal ti! of secondary winding 3'! :oftransw former CT, from the other terminal as of secondary winding 3'? of transformer CT'through limiting resistor RG, one plate of condenser C by Way of terminals 415 and t3, the secondary winding 31 of control transformer CT by way of terminals 39 and 4!, and to the cathode i! of; tube VT! through the other plate of condenserC by Way vof terminals d! and 49. and S2 of transformer CT are arranged and connected so that the energysupplied to the anode of the tube and the bias voltage supplied to the shield grid of the tube are of opposite polarity. That is, when the instantaneous polarity of the alternating current energy supplied from the secondary windings S! and S2 is such that'the anode 5 of tube VT! is positive with respect to the cathode! I, the; biasing voltage supplied from the secondary winding S2 is such that the shield l is negative with respect to thelcathode H.

From the foregoing it will be, seen thatthe circuit network shown in the drawing is arranged and constructed so that the circuit by which energy issupplied to the winding ofirelay R includes in series therewith all other elements of the circuit network, so that if a break de-. velops in any portion of the circuit network, the supply of energy to the relay R will be inter-r rupted, and itsfcontact 33 will release, opening the circuit which is controlled thereby. The secondary. windings S! and S2 are proportioned and arranged so that normally, that is, when no control voltage is supplied to the control grid 9, the bias voltage supplied to the. shield grid l of tube VT! is suflicient to prevent the tube from firing during the alternate half cycles in which the anode 5 is positive with respect to the cathode II.

It will now be assumed that a control voltage of proper phase and voltage value is supplied the other plate of condenser C by way .of terminals 3 and 45, through the limiting resistor RG, through control grid 9 of tube VT! by way ofterminals i9 and 2! to the terminal 29 of:the

secondary Winding S2 of transformer PT, from the otherterminal 3! of secondary winding S2 through the limiting resistor RS, and through the shield grid of tube VT! by way of terminals l! and !5 to the terminal 2? of secondary winding S! of transformer PT. According1y,it will be seen that duringthe half 'cyclesof alternating 1 current energy supplied by the secondary wind--- ing Si, in which the terminal 25 is positive in polarity with respect to the terminal 21, if .the

bias voltage and the control voltage are suitable to cause the tube to conduct, current flows through the circuit traced above to energize reto the primary winding 35 of control transformer CT. Accordingly, a potential is established between the control grid 9 and the cathode I! of tube VTI, since these elements of the tube are connected to the secondary winding 3-! of con--. trol transformer CT by the'circuit including the plates of condenser C', as previously described in connection with tracing the anode circuit. If thepolarity of the alternating currentcontrol voltage supplied at this time is suchthat the control grid dis positive with respect .to

cathode, ii of tube VT! at the time during which the anode 5 is also positive with respect to the cathode II, and if the control voltage supplied to the control grid 9 of tube VT! is of sufficient value to overcome the biasing voltage applied to the shield grid 1, the tube. will conduct and; energy will be supplied to the winding oflrelay The windings S l become conductive.

B and its contact 33 .will be picked up; As previously explained, during the alternate; half cycles in which the polarity of the voltage supplied to the anodei of tube V'Il is negative, so

that the tube cannot conduct, the relay R will remain picked up due to its slow releasing characteristics. Thus, it will be seen that when control voltage of the proper value and phase retionof the circuit is broken, whether the grids become open inside the tube, or if the wirecona nec'tion between the variouselements becomes 1 broken or disconnected, it will be apparent that the supply of energy to the winding of 'relay R.

will be;interrupted, so that contact 33 of relay R will releaseafter a time-interval, and will remain=releasedx Also,'if the supply of biasvoltage --is=interrupted in such manner that the tube might possiblyconduct without the presenceof a positive potential on the control grid 9, thelowimpedance winding 311 and capacity 0,"; as

anode circuit will beopen, and relayR will be released. Likewise, if any of the elements in the control portion of the circuit including the secondary winding 31 of transformer CT, the condenser C, and their connections to the control grid 9 and cathode ll become open, the anode circuit including relay R will be interrupted, so

7 that relayRwill release.

From the foregoing, it will be seen that vacuum tube circuits arranged as shown in the drawing will provide safe operation, and the derangement of any portion of the circuits will be control source and the control grid remained intact, stray high-frequency voltages supplied to the grid of the tube by capacitive coupling effect proposed, if the connection between the source i of control voltage and the cathode of the tube became open while the connection between the were in some cases sufficient to cause the tube to However, in acircuit arranged as shown in the drawing and embodying my invention, I provide condenser C, which is proportioned and arrangedto effectively shunt any such stray voltages which are present in the input circuit including thesecondary winding 31 of transformer CT. It is contemplated that the condenser C will be selected so that it will have sufficient reactance at the frequency of the control voltage to prevent it from shunting the control energy enough to prevent the tube VTI from being properlycontrolled thereby, but that the condenser C will have sufficient capacity to effectively shunt small stray high-frequency voltages which may appear across the secondary winding 31, due to extraneous voltages supplied from the alternating current control source. In order that the presence of condenser C may be checked at all times to insure that stray voltages supplied from the secondary winding 31 will be shunted, the plates of the condenser are each provided with two terminals, and the anodecircuit is carried through each'pl'a'teof the con denser as previously traced. Accordingly, it will be seen that if either plate of condenser C becomes open or if the connections thereto are open or broken, the anode circuit will be interrupted, so that relay R will release if picked up or,-remain released if not picked up.

Since the circuitfor supplyingthe alternating current control voltage to the control grid 9 of tube VTI' is a portion of the series anode circuit previously described, it will be apparent, that should the connection to the control grids be come broken or disconnected, the anode'circuit for the tubewill be interrupted so that relay R. will be released'ifalready picked up or will fail to' picl up, j nccordinglyyno possibility of false; -firing .ofthe tubedue toleaka'ge between. the

anode; 5jor its connections and the controligrid' 9*or. itsconnections can occur since any such leakage current will be shunted by the relatively long as the circuit is intact, so that such leakage current will not develop appreciable voltage between the control grid and cathode sufficient to cause the tube to fire improperly. If thegrid circuit connjectionto capacityC and winding'31 isopen," the anode circuit will also be interrupted at the same point as previouslt po nted The grid protective or limiting resistor RG,

which is included primarily to limit the flow of current between the grid and cathode when the control .grid is at positive potential, may alternatively be connected between the control source and capacitor C, that is, between terminals 39 and 43. The capacitor C would thus be even more effective in shunting stray high-frequency voltages from the control grid.

In vacuum tube circuits ofthe type described it has been the practice to provide a relay which is rendered slow in releasing its contacts by the connection of a condenser, resistor, or a snubbing rectifier across the winding of the relay. Such an arrangement may result in false operation of the relay, since if the snubbing circuit becomes disconnected, the inductive voltage provided by the self-induction of the relay winding when the anode circuit is interrupted may be sufficient to cause the tube to remain in a conductive condition and thus cause the relay to remain picked up. Accordingly, I prefer to provide a relay of the type which is rendered slow in releasing by the provision of a copper ferrule or sleeve surrounding the core structure of the relay, since the possibility of a short, or open circuit in this single-turn copper winding is extremely remote.

From the foregoing,it will be seen that my invention provides an electron tube circuit in which Although the circuits have-been shown and described as employing gas type tubes of {the thyratron type, it is to be understood. that my invention is not limited to this type of tube, and any suitable type of electron tube may be used.

The following values are typical for an electron tube circuit as herein disclosed:

' Tube2D21 miniature thyratron.

' 0 0.005 mm. Notcritical.)

RS-200 ohms."

RP3000 ohms.

Relay1000 ohms winding resistance, slow release type.

Voltage across secondary winding SI of transformer.PT115 volts R. M. S.

Voltage across secondary winding S2 "of trans- -former-PT2.5 volts R. M. S.

With the-above values, thetube will fire and pickuptherelay when the control voltage across terminals 39'and 4! of transformer CT exceeds approximately 6.5. voltsR. M. S. The frequency of the control voltagema'y be any suitable value,

' such as, for, example, 100 cycles per second.

j Although I have herein shown and described only one form of 'electrontube circuitsembodying j my invention, it is to be understoodthat various changes and modifications may be made therein Within ithescope of the appended claim Without departing from the spirit and scope of my invention.

series circuit.

of'the grid in-series between the two terminals, a first source of energy for establishing a positive potential between said anode and said cathode,,--a second source of energy for establishing a negative potential between said shield grid and i said cathode, -a control circuit comprising an impedance across which a control voltage may be developed, a capacitor efiectively connected in multiple with said impedance-with respect to its charging 0r displacement current and with its plates eifectively connected in series with said control circuit, said first'sourceof energy being connected in series to said-anode, said shield grid being connected in series with said first and said second sources, said-control grid being connected-in series with saidsecond source and said control circuit andsaid'cathode being connected in series with said control circuit, whereby all elements of the combination are connected in a PAUL N. r

References Cited in the file of this .patent UNITED STATES PATENTS Name 7 Date. Young Feb. 22,1949 Hart Oct. 11, 1949 Rowe Aug. 3, 1950 Number 

